A PRESSURE FLUID CONTROL SYSTEM

Abstract: A vehicle hood comprises a frame which may be extended by a pair of hydraulically operable rams (1 and 2) from stowed to an extended position and tensioned by a pair of hydraulically operable rams (3 and 4). The rams are supplied in operation with hydraulic fluid by means of a pump (6) through a hydraulic circuit comprising a solenoid operable valve (13) in parallel with a variable restrictor (14). As the hood is extended gravity tends to take over. At that point a microswitch (15) is activated by the hood to close valve (13) thereby lowering the hydraulic fluid flow rate and obviating crashdown of the food.

Description: A PRESSURE FLUID CONTROL SYSTEM The present invention relates to a pressure fluid control system. The system may be used particularly, but not exclusively, for the hood of an automobile. In a known pressure fluid control system for the hood of a convertible of an automobile, the hood comprises a frame which is driven by hydraulic rams from a stowed to an extended position. The supply of hydraulic fluid to the rams is such that as pressure in the system falls, the flow rate increases. Gravity takes over at a position intermediate the stowed and fully extended position causing the pressure to fail and the flow rate therefore to increase. This in turn speeds up the extension of the frame and eventually causes the frame to crash into the windscreen header with possible damage to both header and hood. According to the present invention there is provided a pressure fluid control system comprising a piston and cylinder device, means for supplying fluid under pressure to the device, and valve means for controlling the flow of pressure fluid from the means for supplying to the device, the valve means comprising a valve and a restrictor operative to control the supply of pressure fluid to the device and means for opening and closing the valve in response to a signal representing the position of an object controlled by the device. In a preferred embodiment of the invention, the device is operative to drive an object between first and second positions. The object may, for example, be the frame of a hood of a convertible automobile. The system may be hydraulic or pneumatic. More than one device may be provided. In the case of the hood, two devices may be provided to drive the hood between stowed and extended positions and to tension the hood. The signal representing the position of the hood may be generated by a microswitch. Advantageously the switch is disposed on the rear cantrail pivot of the frame of the hood. The restrictor is advantageously variable. This may be achieved by moving a cone axially with respect to an orifice to produce an annular orifice of varying area. In order that the invention may be more clearly understood, one embodiment thereof will now be described by way of example, with reference to the accompanying drawings, in which:- Figure I shows an existing hydraulic circuit diagram for the motorised hood of a convertible automobile, Figure 2 shows the diagram of Figure I modified according to the invention. Figure 3 is a cross-sectional view of a valve block forming part of the system of Figure 2. Figure 4 diagrammatically shows the frame of a hood mechanism from an automobile in a stowed condition. Figure 5 diagrammatically shows the frame of Figure 4 partially extended, Figure 6 diagrammatically shows the frame of Figures 4 and 5 fully extended, and Figure 7 diagrammatically shows a vehicle hood of which the frame of Figures 4, 5 and 6 forms part. Referring to Figure I, the existing hydraulic system has a pair of hydraulically operable hood rams I and 2 and a pair of hydraulically operable tensioning rams 3 and 4. The rams of each pair are disposed on opposite sides respectively of the hood. Hydraulic fluid is fed to these rams by means of an electrically operated power pack 5 comprising a d.c. motor driven pump 6 via appropriate hydraulic fluid lines which incorporate five lowering valves 7,8,9,10 and II. The pressure/flowrate relationship of the system is such that the pressure fluid (hydraulic) flow rate increases as the pressure in the system falls. In operation of the hood hydraulic fluid is fed to the rams I and 2. Gravity begins to assist the extension of the hood frame when the frame reaches the position shown in Figure 5 from the stowed position shown in Figure 4. This causes the hydraulic fluid pressure to fall and the fluid flow rate to increase. This leads to the hood speeding up and eventually crashing into the automobile windscreen header with possible damage to both header and hood in the position shown in Figure 6. Figure 2 shows the diagram of Figure I modified to overcome this problem. In the two figures equivalent parts bear the same reference numerals. The modification comprises a new valve block 12. This new block 12 comprises a two stage pressure lowering solenoid 15 operable valve 13 and a variable restrictor 14 connected in parallel with this valve. The valve 13 which is initially open as the hood is being raised is operated by a microswitch 15 which senses the position of the rear cantrail 16 of the frame 17 of the hood. When the cantrail reaches the position shown in Figure 5, the position in which gravity begins to take over, the microswitch 15 is activated to close valve 13. This creates a higher pressure in the system thereby lowering the hydraulic fluid flow rate and obviating crashdown. The back pressure may be adjusted by adjusting the restrictor 14. The restrictor comprises a conical member which is axially adjustable with respect to an orifice. The area available for fluid flow is increased or decreased by moving the cone into or out of the orifice. The resultant annular orifice reduces any tendency there might otherwise be for a blockage to occur. The block 12 has three ports respectively referenced PI, P2 and P3 in Figure 2. When valve 13 is opened electrically fluid flow is possible in both directions from both P2 and P3 to PI. When the valve is closed (de- energised) as described above, fluid flow is possible in the direction from PI to P2 and P3 via valve 13 but not possible in the opposite direction so that any flow in this direction is via the restrictor 14. It will be appreciated that the above embodiment has been described by way of example only and that many variations are possible without departing from the scope of the invention. For example, the invention is applicable to any hydraulic or pneumatic control system.

Claims: CLAIMS 1. A pressure fluid control system comprising a piston and cylinder device (l,2), means for supplying fluid (5,6) under pressure to the device, and valve means (7,8,9,10,11 ) for controlling the flow of pressure fluid from the means for supplying to the device, characterised in that the valve means comprising a valve (7, 8,9,10, II) and a restrictor (14) operative to control the supply of pressure fluid to the device and means for opening and closing the valve in response to a signal representing the position of an object controlled by the device. 2. A pressure fluid control system as claimed in claim I, in which the restrictor is variable. 3. A pressure fluid control system as claimed in claim I, in which the restrictor comprises a cone defining with a member an annular orifice. 4. A pressure fluid control system as claimed in claim 3, in which the cone is moveable with respect to the member to vary the area of the orifice. 5. A pressure fluid control system as claimed in any preceding claim, which is hydraulic. 6. A pressure fluid control system as claimed in any of claims I to 4 which is pneumatic. 7. A hood comprising a pressure fluid control system as claimed in any preceding claim, in which the object controlled comprises a frame of the hood. 8. A hood as claimed in claim 7, in which there are two pressure fluid operable rams (1,2) disposed on opposite sides respectively of the hood operative to drive the hood been stowed and extended positions. 9. A hood as claimed in claim 7 or 8, in which there are two pressure fluid operable rams (3,4) disposed on opposite sides respectively of the hood operative to tension the hood. 10. A hood as claimed in claim 7,8 or 9, in which the means for supplying fluid under pressure comprises an electric motor driven pump (6). 11. A hood as claimed in claim 7,8,9 or I0, in which a microswitch (15) is disposed for actuation by the hood operative to generate the signal representing the position of the hood. 12. A hood as claimed in claim II, in which the valve means comprise a number of lowering valves (7,8,9,10 and II) which are disposed in fluid lines to the piston and cylinder device (1,2,3,4) and a two stage pressure lowering solenoid operable valve 13 and the variable restrictor (14) is connected in parallel with this valve, the arrangement being such that after the hood is initially extended the microswitch (15) is activated to close the solenoid operable valve (13) creating a higher pressure in the system thereby lowering the hydraulic fluid flow rate and obviating crashdown of the hood.

Inventors: RAWLINSON NEIL, RAWLINSON, NEIL
Applicants: RAWLINSON NEIL, ROLLS ROYCE MOTOR CARS, RAWLINSON, NEIL, ROLLS-ROYCE MOTOR CARS LIMITED
Application year: 1994
Main classification: B60J7
IPC codes: B60J7, E05F15, F15B11, F16K1, F16K31